The present invention relates generally to a parking brake assembly. More particularly, the present invention relates to a parking brake assembly for an air actuated disc brake.
Air actuated disc brakes are typically used in heavy vehicle applications, such as for braking trucks or buses. Such brakes typically operate as follows. Pressurised air is introduced behind a diaphragm of an air chamber, which generates a load in a push rod. The push rod in turn applies a force to a pivotably mounted operating shaft, causing it to rotate. By means of an eccentric action, an amplified force is applied to one or more tappet assemblies that advance a brake pad towards a brake rotor. This causes a clamping effect on the brake rotor, thereby retarding rotation of the rotor due to friction generated between the brake pad in contact with the tappet assembly and a further brake pad mounted on an opposite face of the brake rotor.
To comply with safety legislation, when a vehicle fitted with air actuated brakes is parked, the brakes must be applied mechanically without reliance on the pressurised air to overcome the risk of the brake force being removed due to accidental leakage of the air, with obvious consequences.
Conventionally, in air actuated brakes of the type described above, the parking brake function is achieved by the addition of a large spring to the rear of the air chamber that generates a load on the push rod when no pressurised air is present.
The addition of the spring, together with an additional air chamber required to release the parking brake that is mounted behind the air chamber for the application of service brakes, adds to the bulk, weight and expense of the vehicle braking system.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.